ath79: phy-ar7200-usb: do not print error on defered init

This is only a cosmetic correction, as the driver works as expected.
However, the error message confuses users about a missing reset definition.

On a defered init we don't see the following error message now:
[    0.078292] ar7200-usb-phy usb-phy: phy reset is missing

Tested-by: Lech Perczak <lech.perczak@gmail.com>
Signed-off-by: Johann Neuhauser <johann@it-neuhauser.de>